Known gill nets have a top corkline consisting of a rope carrying spaced floats, a bottom lead line, usually a rope with internal weights, and a central net or web. The top and bottom selvages of the web can be connected, respectively, to the corkline and lead line by separate hanging cords. To prevent bunching of the net, the hanging cords must be securely knotted to the corkline and lead line at substantially uniformly spaced locations.
The completed setup or shackel of gill net can be large. For example, for salmon fishing in the Bristol Bay area of Alaska the completed shackel can be 50 fathoms (76.2 meters) long and 5 to 10 fathoms (7.6 to 15.2 meters) deep. The web itself can be rolled or folded to compact condition, but the lead line and particularly the corkline are bulky.
The mesh size of the web desired depends on the size and species of the fish to be caught. Again using the example of salmon fishing in Bristol Bay, different webs may be desired for reds (sockeye), pinks (chum), silvers (Coho) and kings (Chinook). Changing webs on short notice, such as before the next tide change, may result in a greatly increased catch.
Government regulations and storage space may limit the number of complete shackels available on board, and fishing may be conducted in an area remote from shore storage or even from a tender where additional shackels might be kept. There also is substantial additional expense in acquiring, maintaining and storing additional shackels for the purpose of having webs of different mesh size conveniently available, as compared to hanging different webs from the same corkline and lead line.
For known hanging systems, it is a complicated and time-consuming process to uncouple a web from its corkline and lead line and rehang a new web. In addition, damage can occur to the corkline, web or lead line even when such process is performed by an experienced worker. Further, the time lost in changing webs can be extremely frustrating to a fisherman, particularly considering the shorter fishing seasons that can be imposed by the government.